The present invention relates to a process for the preparation of oligomers of xcex1-hydroxy carboxylic acids and xcex1-amino acids and to compositions containing such oligomers.
In an effort to improve nutrition, the diets of ruminant animals have been supplemented with proteins and naturally occurring xcex1-amino acids. Unfortunately, these proteins and xcex1-amino acids can be subjected to extensive degradation in the rumen by ruminal microorganisms, thereby rendering the protein or amino acid unavailable to the animal for absorption. This is not a very efficient utilization of the feed, which is especially problematic in animals having increased nutritional requirements such as lactating dairy cows and fast growing animals such as beef cattle.
One approach to solving this problem has been to modify or protect the dietary protein or amino acid by a variety of chemical and physical methods so that it escapes degradation in the rumen. For example, heating soybean meal has shown some promise in producing protected proteins however the results were highly variable. Underheating the protein resulted in no protection while overheating the protein resulted in the degradation of important essential amino acids. See, for example, Plegge, S. D., Berger, L. L. and Fahey Jr. G. C. 1982. Effect of Roasting on Utilization of Soybean Meal by Ruminants. J. Anim. Sci. 55:395 and Faldet, M. A., Son, Y. S. and Satter, L. D. 1992. Chemical, in vitro and in vivo evaluation of soybean heat-treated by various processing methods. J. Dairy Sci. 75:789. Similarly, physical coating of proteins with materials such as fats and calcium soaps of fats has been with mixed success.
Therefore, there is a need to somehow protect the protein from degradation in the rumen in order to make it available to the animal in the intestine where it can be properly absorbed. This would allow the animal to get increased nutritional benefit from the feed. Increasing the nutritional benefit of the feed can reduce the amount of feed required by the animals.
The role played by short chain peptides and their derivatives in the areas of nutrition science, flavor chemistry and pharmacology has primed the advances in peptide chemistry. The inherent advantages of enzymatic peptide synthesis has led to it""s evolution as an alternative to chemical coupling methods (Fruton, J. S., 1992, Adv. Enzymology, 53, 239-306). The thiol-protease papain is reported to be the most efficient catalyst for aqueous phase synthesis of homooligomers of hydrophobic amino acids like leucine, methionine, phenylalanine and tyrosine (A. Ferjancic, A. Puigserver and H.Gaertner, Biotech. Lett, 13(3) (1991) 161-166). The equilibria of such reactions is tilted in favor of synthesis by the precipitation of hydrophobic oligomers. However, the difficulty involved in the analysis of higher order, water insoluble oligomers, presents an unique challenge to biochromatography.
Among the objects of the present invention, therefore, is the provision of an oligomer which is protected from degradation in the rumen of a ruminant, the provision of such an oligomer which provides nutritional or pharmacological benefit to the animal, and the provision of a process for the preparation of such oligomers.
Briefly, therefore, the present invention is directed to a composition comprising the oligomeric segment xe2x80x94CAxe2x80x94(AA)nxe2x80x94wherein CA is the residue of an xcex1-hydroxy carboxylic acid, each AA is the residue of an xcex1-amino acid independently selected from the group consisting of xcex1-amino acids, n is at least 1 and CA is bonded to (AA)n by an amide linkage.
The present invention is further directed to a process for the preparation of an oligomer. The process comprises preparing a mixture containing (i) an enzyme, (ii) an xcex1-hydroxy carboxylic acid and (iii) an xcex1-amino acid or a peptide oligomer. The xcex1-hydroxy carboxylic acid and the xcex1-amino acid each are present in the mixture as a free acid, acid halide, amide, ester or anhydride independently of the other. The process further comprises forming an amide linkage between the residue of the xcex1-hydroxy carboxylic acid and the residue of the xcex1-amino acid or the peptide oligomer.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.